U.S. patent application number 09/852379 was filed with the patent office on 2002-11-14 for process for multi-layer coating.
Invention is credited to Kimpel, Matthias, Reis, Oliver, Wulf, Martin.
Application Number | 20020166770 09/852379 |
Document ID | / |
Family ID | 25313160 |
Filed Date | 2002-11-14 |
United States Patent
Application |
20020166770 |
Kind Code |
A1 |
Kimpel, Matthias ; et
al. |
November 14, 2002 |
Process for multi-layer coating
Abstract
A process for the production of a multi-layer coating, wherein a
primer layer which is electrically conductive in the at least
partially cured state is applied by electrodeposition from an
electrodeposition coating agent (I) to an electrically conductive
three-dimensional object, at least partially cured exclusively by
the action of near infra-red radiation substantially only on the
surfaces of the object exposed to the radiation, and an additional
coating layer is applied by electrodeposition from an
electrodeposition coating agent (II) which is different from
electrodeposition coating agent (I), and then this additional
coating layer as well as completely uncured or incompletely cured
area parts of the primer layer produced from electrodeposition
coating agent (I) are cured.
Inventors: |
Kimpel, Matthias; (Schwelm,
DE) ; Wulf, Martin; (Wuppertal, DE) ; Reis,
Oliver; (Witten, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
25313160 |
Appl. No.: |
09/852379 |
Filed: |
May 10, 2001 |
Current U.S.
Class: |
204/478 ;
204/479; 204/488; 204/493; 204/500 |
Current CPC
Class: |
B05D 1/007 20130101;
B05D 7/546 20130101; B05D 3/0263 20130101; C25D 13/00 20130101 |
Class at
Publication: |
204/478 ;
204/479; 204/488; 204/493; 204/500 |
International
Class: |
C25D 013/06; C23C
028/00; C25D 013/12 |
Claims
1. A process for the production of a multi-layer coating on the
surfaces of an electrically conductive three dimensional object
comprising the following steps: (1) applying at least one primer
layer to the surfaces of the object by electrodeposition from an
electrodeposition coating agent (I); (2) at least partially curing
exclusively by the action of near infra-red radiation substantially
only the primer layer on the surfaces of the object exposed to said
radiation to form a primer layer that is electrically conductive in
the at least partially cured state; (3) applying an additional
layer of coating by electrodeposition from an electrodeposition
coating agent (II) which is different from electrodeposition
coating agent (I) over the primer layer applied in step (1) that is
at least partially cured; and (4) curing both the primer layer and
the additional layer on the object to form the multilayer coating
on the object.
2. The process of claim 1 wherein more than one primer layer is
applied to the surfaces of the object by electrodeposition and each
layer is at least partially cured exclusively with near infra-red
radiation after application of the primer layer.
3. The process of claim 1 wherein prior to curing the primer and
the additional layer in step (4) at least one additional layer of
coating is applied.
4. The process of claim 1 wherein after curing the primer and the
additional layer in step (4) at least one additional layer is
applied.
5. The process of claim 1 wherein curing of the primer and the
additional layer in step (4) is accomplished by baking at an
elevated temperature.
6. The process of claim 1 wherein the electrodeposition coating
agents (I) and (II) are different from one another and are
individually selected from the group consisting of anodically
electrodepositable coating agents and cathodically
electrodepositable coating agents.
7. The process of claim 1 wherein the primer layer from
electrodeposition coating agent (I) in the at least partially cured
state has a volume resistivity from 10.sup.3 to 10.sup.8
Ohm.multidot.cm.
8. The process of claim 1 where the three dimensional objects have
visible and non visible surface regions and are selected from the
group consisting of automotive bodies, automotive body parts, truck
chassis, agricultural machines, household appliance housings and
small bulk goods.
9. The process of claim 1 wherein the near infra-red radiation is
infra-red radiation in the wave length range from 750 nm to 1500
nm.
10. The process of claim 1 wherein the near infra-red radiation is
provided by near infra-red radiation emitters with an intensity of
more than 10 kW/m.sup.2 to 10 MW/m.sup.2.
11. A process for the production of a multi-layer coating on the
surfaces of an electrically conductive three dimensional object
comprising the following steps: (1) applying a primer layer to the
entire surface of the object by a single electrodeposition from an
electrodeposition coating agent (I); (2) at least partially curing
exclusively by the action of near infra-red radiation substantially
only the primer layer on the surfaces of the object exposed to said
radiation to form a primer layer that is electrically conductive in
the at least partially cured state; (3) applying a second layer of
coating by electrodeposition from an electrodeposition coating
agent (II) which is different from electrodeposition coating agent
(I) over the primer layer applied in step (1) that is at least
partially cured; and (4) curing both the primer layer and second
layer on the object to form the multilayer coating on the
object.
12. The process of claim 11 wherein prior to curing the primer and
second layer in step (4) at least one additional layer of coating
is applied.
13. The process of claim 11 wherein after curing the primer and
second layer in step (4) at least one additional layer is
applied.
14. The process of claim 11 wherein curing of the primer and second
layer in step (4) is accomplished by baking at an elevated
temperature.
15. The process of claim 11 wherein the electrodeposition coating
agents (I) and (II) are different from one another and are
individually selected from the group consisting of anodically
electrodepositable coating agents and cathodically
electrodepositable coating agents.
16. The process of claim 11 wherein the primer layer from
electrodeposition coating agent (I) in the at least partially cured
state has a volume resistivity from 10.sup.3 to 10.sup.8
Ohm.multidot.cm.
17. The process of claim 11 where the three dimensional objects
have visible and non visible surface regions and are selected from
the group consisting of automotive bodies, automotive body parts,
truck chassis, agricultural machines, household appliance housings
and small bulk goods.
18. The process of claim 11 wherein the near infra-red radiation is
infra-red radiation in the wave length range from 750 nm to 1500
nm.
19. The process of claim 11 wherein the near infra-red radiation is
provided by near infra-red radiation emitters with an intensity of
more than 10 kW/m.sup.2 to 10 MW/m.sup.2.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a process for the production of a
two-layer electrodeposition coating on three-dimensional
electrically conductive objects.
BACKGROUND OF THE INVENTION
[0002] The production of two-layer electrodeposition coatings is
known in the prior art. For example, multi-layer coatings composed
of a two-layer electrodeposition coating which is overcoated with a
clear coat or a base coat/clear coat layer are known from U.S. Pat.
No. 5,908,667 and U.S. Pat. No. 5,882,734.
[0003] In the conventional production of two-layer
electrodeposition coatings, an electrodeposition coat primer layer
is initially deposited from an electrodeposition coating agent
containing electrically conductive constituents on a metal
substrate. After the electrodeposition coating layer has been cured
by stoving (baking), the latter is sufficiently electrically
conductive for a second electrodeposition coating layer to be
deposited on it electrophoretically from a second electrodeposition
coating agent and likewise stoved (baked). Overcoating with further
coating layers may then take place.
[0004] This invention further develops the coating process of the
prior art for coating three-dimensional objects having surface
regions that are visible and not visible to the observer and saves
electrodeposition coating agent and simplifies the coating
process.
SUMMARY OF THE INVENTION
[0005] The invention relates to a process for the production of a
multi-layer coating in which a primer layer that is electrically
conductive in the at least partially cured state is applied by
electrodeposition from an electrodeposition coating agent (I) to an
electrically conductive three-dimensional object, at least
partially cured exclusively by the action of near infra-red
radiation substantially only on the surfaces of the object exposed
to the radiation, and an additional coating layer is applied by
electrodeposition from an electrodeposition coating agent (II) that
is different from electrodeposition coating agent (I), and then
this additional coating layer as well as completely uncured or
incompletely cured area parts of the primer layer produced from
electrodeposition coating agent (I) are cured.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0006] In the description and claims, the phrase "at least partial
curing" is used. "At least partial curing" means "partial curing"
or preferably "complete curing". "Partial curing" means a minimum
degree of curing of the electrodeposition coat primer layer that
leads to a volume resistivity that is sufficiently low, for
example, from 10.sup.3 to 10.sup.8 Ohm.multidot.cm, for the
electrophoretic deposition of a further coating layer from an
electrodeposition coating agent. In connection with the present
invention, "partial curing" expressly does not mean degrees of
curing of the electrodeposition coat primer layer that do not lead
to a volume resistivity that is sufficiently low for the
electrophoretic deposition of an additional coating layer from an
electrodeposition coating agent; rather, the term "insufficient
curing" is used in that case in order to make a clear
distinction.
[0007] The application of the primer layer applied from
electrodeposition coating agent (I) may take place in operating
steps repeated several times, for example, up to three times in
succession, a fresh electrodeposition coating from
electrodeposition coating agent (I) taking place after exposure to
near infra-red irradiation (NIR irradiation) in each case. In so
doing, a multiple deposition of an electrodeposition coating layer
from electrodeposition coating agent (I) may be obtained only on
area parts of the coating layer(s) produced from electrodeposition
coating agent (I) that have been at least partially cured by NIR
irradiation, whereas completely uncured or insufficiently cured
parts of the surface do not undergo multiple coating from
electrodeposition coating agent (I). An electrodeposition
coat-primed object having a layer thickness of the
electrodeposition coat primer that is greater at least on the
visible surfaces of the object than on the non-visible or not
immediately visible surfaces of the object may thus be
obtained.
[0008] The embodiment of the process according to the invention in
which the electrodeposition coat primer layer is applied by only a
single electrodeposition from electrodeposition coating agent (I)
is preferred. This is a process for the production of a multi-layer
coating in which a primer layer that is electrically conductive in
the at least partially cured state is applied by electrodeposition
from an electrodeposition coating agent (I) to the entire surface
of an electrically conductive three-dimensional object. This
electrodeposited primer layer is at least partially cured
exclusively by the action of near infra-red radiation substantially
only on the surfaces (visible surfaces) of the object exposed to
the radiation, then a second coating layer is applied by
electrodeposition from an electrodeposition coating agent (II),
which is different from electrodeposition coating agent (I), and
then the second coating layer as well as completely uncured or
incompletely cured area parts of the electrodeposition coat primer
layer are cured.
[0009] In the process according to the invention, electrodeposition
coating agents (I) and (II) that are inherently known but different
from one another are used. In both cases, they may be
electrodeposition coating agents that can be deposited anodically
or cathodically. Electrodeposition coating agent (I) contains
constituents that provide the primer layer, in the at least
partially cured state, a volume resistivity that is sufficiently
low for the electrodeposition of a further coating layer from an
electrodeposition coating agent.
[0010] Electrodeposition coating agents (I) and (II) are waterborne
coating agents with a solids content of, for example, 10 wt. % to
30 wt. %. The solids are composed of resin solids, at least in the
case of electrodeposition coating agent (I), also of electrically
conductive constituents and optionally fillers, pigments and
conventional non-volatile paint additives. The resin solids
themselves are composed of one or more conventional binders, at
least a part of the binders carrying ionic substituents and/or
substituents that can be converted to ionic groups, and groups
capable of chemical crosslinking. The binders having groups capable
of chemical crosslinking may be self-crosslinking binders or they
may be externally crosslinking binders. In the case of externally
crosslinking binders, they are used in combination with
crosslinking agents.
[0011] For example, conventional anodically electrodepositable
(AED) coating agents may be used as electrodeposition coating agent
(I) and/or (II). AED coating agents contain, for example, binders
based on polyesters, epoxy resin esters, (meth)acrylic copolymer
resins, maleinate oils or polybutadiene oils with a weight-average
molecular mass (Mw) of, for example, 300 to 10,000 and an acid
value from 35 to 300 mg KOH/g. The binders carry --COOH,
--SO.sub.3H and/or --PO.sub.3H.sub.2-groups and, after
neutralization of at least a part of the acid groups with bases,
particularly amines, may be converted to the aqueous phase. The
binders may be self-crosslinking or externally crosslinking. The
AED coating agents may therefore also contain conventional
crosslinking agents, e.g., triazine resins, crosslinking agents
containing groups capable of transesterification, or blocked
polyisocyanates.
[0012] The conventional cathodically electrodepositable (CED)
coating agents based on CED binders may also be used as
electrodeposition coating agent (I) and/or (II). The CED binders
contain one or more cationic or basic groups, for example, primary,
secondary and/or tertiary amino and/or ammonium, e.g., quaternary
ammonium, phosphonium and/or sulfonium groups. The CED binders
have, for example, amine values from 20 to 250 mg KOH/g and
weight-average molecular masses (Mw) of preferably 300 to 10,000.
Neutralizing agents used for the CED binders are the conventional
acids for CED coating agents, such as, formic acid, acetic acid,
lactic acid, methanesulfonic acid. Examples of CED binders include
aminoepoxy resins, aminoepoxy resins with terminal double bonds,
aminoepoxy resins with primary OH groups, aminopolyurethane resins,
amino group-containing polybutadiene resins or modified epoxy resin
carbon dioxide amine reaction products, and amino(meth)acrylate
resins. The CED binders may be self-crosslinking or they may be
used in mixture with well known crosslinking agents. Examples of
such crosslinking agents include aminoplastic resins, blocked
polyisocyanates, crosslinking agents with terminal double bonds,
polyepoxy compounds or crosslinking agents containing groups
capable of transesterification.
[0013] Electrodeposition coating agent (I) contains one or more
electrically conductive constituents. They confer on the
electrodeposition coating layer in the at least partially cured
state deposited from electrodeposition coating agent (I) a volume
resistivity, which is sufficiently low, for example, from 10.sup.3
to 10.sup.8 Ohm.multidot.cm, for the electrophoretic deposition of
a further coating layer from an electrodeposition coating agent.
Examples of such constituents are particulate inorganic or organic
electrical conductors or semi-conductors, such as, black iron
oxide, graphite, conductive carbon black, metal powder, e.g., of
aluminum, copper or refined steel, molybdenum disulfide or
electrically conductive polymers, such as, e.g., preferably
polyaniline. Examples of electrodeposition coating agents
containing such constituents which may be used as electrodeposition
coating agent (I) can be found in U.S. Pat. No. 3,674,671; GB
2,129,807; U.S. Pat. Nos. 4,882,090; 4,988,420 and U.S. Pat. No.
5,275,707. The electrically conductive constituents are contained
in electrodeposition coating agent (I) in a quantity such as to
obtain the sufficiently low volume resistivity of the primer layer
in the at least partially cured state deposited therefrom. Based on
the solids content of electrodeposition coating agent (I), the
proportion of electrically conductive constituent(s) is, for
example, from 0.5 to 30 wt. %. The proportion may be determined
easily by the skilled person; it depends, for example, on the
specific gravity, the specific electrical conductivity and the
particle size of the electrically conductive constituents used.
[0014] In addition to the binders and optionally present
crosslinking agents and the electrically conductive constituents
contained necessarily in electrodeposition coating agent (I) and
optionally, in electrodeposition coating agent (II),
electrodeposition coating agents (I) and (II) may contain color-
and/or special effect-imparting pigments, fillers, and/or
conventional paint additives, in each case in conventional quantity
proportions for electrodeposition coating agents.
[0015] The pigment plus filler/binder plus crosslinking agent
weight ratio of electrodeposition coating agents (I) and (II) is,
for example, 0:1 to 0.8:1; it should be borne in mind here that the
electrically conductive constituents in electrodeposition coating
agent (I) in the context of the present invention are not
considered as belonging to the group of pigments and fillers.
Examples of pigments and fillers include conventional inorganic
and/or organic colored pigments and/or special-effect pigments such
as, titanium dioxide, iron oxide pigments, carbon black,
phthalocyanine pigments, quinacridone pigments, metallic pigments,
e.g. of aluminum, interference pigments, such as, titanium
dioxide-coated aluminum, coated mica, iron oxide in flake form,
copper phthalocyanine pigments in flake form, kaolin, talc or
silica.
[0016] Electrodeposition coating agents (I) and (II) may contain
additives, for example, in quantity proportions from 0.1 wt. % to 5
wt. %, based on the resin solids. Examples of additives include
wetting agents, neutralizing agents, leveling agents, catalysts,
corrosion inhibitors, anti-foaming agents, organic solvents, light
stabilizers and antioxidants.
[0017] The objects coated in the process according to the invention
are electrically conductive, three-dimensional objects with surface
regions which are visible and not visible to the observer. Examples
include electrically conductive polymer substrates, substrates
constructed on a composite basis from electrically conductive
polymer substrates and metals, and in particular metal substrates,
for example, automotive bodies or parts thereof, truck chassis,
agricultural machines, household appliance housings but also small
bulk goods with visible and non visible surface regions. Visible
surfaces are, in particular, immediately visible surfaces. Examples
of visible surfaces of an automotive body include, in particular,
its immediately visible outer skin and also visible interior
surfaces, for example, surfaces that are visible when the doors are
opened, such as, sills. Non visible or not immediately visible
surface regions include interior surfaces, for example, of hollow
areas, and also other surfaces that are not directly accessible.
Examples of non visible or not immediately visible surfaces of an
automotive body include surfaces in the interior of an automotive
body, for example, motor space, passenger space or trunk, interior
surfaces of hollow areas and the outward facing surface of the
underbody.
[0018] The electrodeposition coat primer layer is applied in the
usual way by electrodeposition from electrodeposition coating agent
(I) to the entire surface of the three-dimensional objects,
adhering electrodeposition coat bath material is removed in the
usual way, and at least partial curing is then carried out
substantially only on the visible surfaces exclusively by the
action of NIR (near infra red) radiation, i.e., only or
substantially only the visible surfaces of the object are
irradiated with NIR radiation. In the preferred embodiment of the
process according to the invention, the dry layer thickness of the
electrodeposition coat primer layer is, for example, 5 .mu.m to 25
.mu.m.
[0019] The NIR radiation used in the process according to the
invention must not be confused with longer-wave IR radiation;
rather, it is short-wave infra-red radiation in the wave length
range from about 750 nm to about 1500 nm, preferably 750 nm to 1200
nm. Radiation sources for NIR radiation include, for example,
conventional NIR radiation emitters which may emit radiation as a
flat, linear or point source. NIR radiation emitters of this kind
are available commercially (for example, from Adphos). They are,
for example, high-performance halogen radiation emitters with an
intensity (radiation output per unit area) of generally more than
10 kW/m.sup.2 to, for example, 10 MW/m.sup.2, preferably from 100
kW/m.sup.2 to 800 kW/m.sup.2. For example, the radiation emitters
reach a radiation emitter surface temperature (coil filament
temperature) of more than 2000.degree. K, preferably more than
2800.degree. K, particularly more than 2900.degree. K, e.g., a
temperature from 2000 to 3500.degree. K. Suitable radiation
emitters have, for example, an emission spectrum with a maximum
between 750 nm and 1200 nm.
[0020] NIR irradiation may be carried out, for example, in a belt
unit fitted with one or more NIR radiation emitters or with one or
more NIR radiation emitters positioned in front of the
three-dimensional object to be irradiated, or the object to be
irradiated and/or the NIR radiation emitter(s) is(are) moved
relative to one another during irradiation. For example, the object
to be irradiated may be moved through an irradiation tunnel fitted
with one or more NIR radiation emitters, and/or a robot fitted with
one or more NIR radiation emitters may guide the NIR radiation
emitter(s) over the surface to be irradiated, for example, in the
manner of a silhouette-like guiding of the NIR radiation
emitters.
[0021] In principle, the irradiation time, distance from the
object, radiation output and/or radiation emitter surface
temperature of the NIR radiation emitter may be varied during NIR
irradiation. The distance between the object and NIR radiation
emitter may be, for example, 2 cm to 60 cm. NIR irradiation may
take place continuously or discontinuously (in cycles). The
irradiation time may be, for example, from 1 to 100 seconds,
preferably not more than 60 seconds. The irradiation time refers
either to the duration of continuous irradiation or to the sum of
the periods of different irradiation cycles. By selecting the
various parameters in a controlled manner, different surface
temperatures of the electrodeposition coat primer layer may be
obtained, for example, surface temperatures from 100.degree. C. to
300.degree. C.
[0022] The various irradiation parameters, such as belt speed or
irradiation time, distance from object, radiation output of the NIR
radiation emitter used, may be adapted by the skilled person
according to the requirements of the coating task in question.
[0023] In contrast to a conventional curing of the
electrodeposition coat primer layer by stoving (baking at an
elevated temperature) with convection and/or irradiation with
conventional longer-wave IR radiation, the NIR radiation acting
only for a short period and only or substantially only on the
visible object surfaces does not permit partial or full curing of
the electrodeposition coat primer layer on the entire surface of
the three-dimensional object. Rather, an object provided with an at
least partially cured electrodeposition coat primer on the visible
surfaces is obtained, whilst the electrodeposition coat primer
layer on the non visible or not immediately visible surfaces of the
object may be at least partially cured over area parts but is
completely uncured or insufficiently cured over a substantial
proportion of its area. Depending on the object geometry and
circumstances during NIR irradiation, the completely uncured or
insufficiently cured proportion of the area may account for, for
example, 10% to 80% of the electrodeposition coat primer covering
the entire object surface. Only the parts of the surface provided
with an at least partially cured electrodeposition coat primer
layer have a sufficiently low volume resistivity and can
subsequently be coated with electrodeposition coating agent (II).
Compared with the procedure characterized by conventional curing,
savings can therefore be made on electrodeposition coating agent,
particularly electrodeposition coating agent (II), in the process
according to the invention.
[0024] As a result of the procedure according to the invention, a
coating covering the entire object surface with the
electrodeposition coating layer applied from electrodeposition
coating agent (II) may be avoided. If it is desired to carry this
out during the conventional production of two-layer
electrodeposition coatings, this can be achieved by means of
process measures during the electrodeposition of the second
electrodeposition coat layer and/or by means of a special
formulation of the second electrodeposition coating agent. These
restrictive means, however, need not be used with the process
according to the invention.
[0025] In the process according to the invention, in contrast to
the process of the prior art, no stoving (baking) oven is required
for the separate curing of the electrodeposition coat primer
layer.
[0026] The three-dimensional object provided with the
electrodeposition coat primer layer does not become as hot on the
whole during NIR irradiation as it does with conventional curing.
The cooling time prior to further electrodeposition of coating from
electrodeposition coating agent (II) is reduced in the process
according to the invention compared with the conventional process.
This permits an increase in productivity, particularly with the
two-layer electrodeposition coating of objects that require a long
cooling period after conventional stoving (baking).
[0027] After completion of the final or, in the preferred
embodiment of the process of the invention, the sole NIR
irradiation step, further coating is carried out with
electrodeposition coating agent (II). The second electrodeposition
coating layer is electrodeposited in the usual way in a dry layer
thickness of, for example, 10 .mu.m to 45 .mu.m, preferably from 15
.mu.m to 30 .mu.m, and then cured. Curing of the second
electrodeposition coating layer may take place in a similar way to
the electrodeposition coat primer by means of NIR irradiation, but
in that case entails a subsequent additional stoving (baking) step
in order to cure hitherto uncured or incompletely cured area parts
of the electrodeposition coat primer layer, and optionally uncured
or incompletely cured area parts of the second electrodeposition
coating layer. Curing therefore takes place, preferably by stoving
(baking), with convection and/or IR irradiation, for example, at
object temperatures from 130.degree. C. to 180.degree. C. In so
doing, hitherto uncured or incompletely cured area parts of the
electrodeposition coat primer layer are cured in one process step
together with the second electrodeposition coating layer.
[0028] As a result of the procedure according to the invention, a
three-dimensional object is obtained with an electrodeposition coat
primer covering the entire object surface and a second
electrodeposition coating layer not extending over the entire
object surface, i.e., applied only or substantially only to the
visible surfaces.
[0029] If the coating layer applied from electrodeposition coating
agent (II) is not an external clear coat or top coat layer, at
least one further coating layer may be applied. Optionally, this
may take place in the wet-in-wet process, i.e. before stoving
(baking) of the electrodeposition coating layer applied from
electrodeposition coating agent (II). The application of the at
least one further coating layer takes place, preferably only or
substantially only, on surface regions visible to the observer. For
example, the coating layer applied from electrodeposition coating
agent (II) may act as the color shade-determining base coat layer
and may be overcoated with a clear coat layer, or it may act as the
primer surfacer layer and be overcoated with a top coat layer or a
base coat/clear coat two-layer coating.
[0030] The process according to the invention makes it possible to
carry out the two-layer electrodeposition coating inherently well
known for coating three-dimensional substrates with the smallest
possible consumption of electrodeposition coating agent,
particularly electrodeposition coating agent used for the
production of the second electrodeposition coating layer. Moreover,
a procedure with increased productivity compared with the prior art
may be achieved due to the possibility of coating with the second
electrodeposition coating agent after a shorter cooling period.
* * * * *